The present invention relates to a turbopump sealing device, more particularly for equipping liquid propergol supply units for rocket motors.
It is known that modern rocket motors using liquid propergols, usually oxygen and hydrogen, are equipped with pumps for conveying the fluid (liquid hydrogen) and the oxidant (liquid oxygen) from the reservoirs to the combustion chamber at a given pressure and flow rate. These pumps are driven directly or through a gear box by a turbine operating from combustion gases supplied by a gas generator or combustion prechamber. The shaft common to the pump and to the turbine is supported by bearings usually lubricated by a flow of hydrogen, all or part of which is discharged during operation of the motor towards the turbine compartment.
Whether it is a turbine between two bearings or cantilevered, with a single bearing, there should be incorporated between the bearing and the turbine a sealing means having a dual role:
(a) cold period:
This is the period preceding start up of the motor in which the turbopump is placed in contact with the ergols at very low temperature and at a relatively low pressure, close to that of the reservoirs, so that on start up of rotation thermal operating conditions are already established close to those of operation.
During this phase, the sealing means for safety reasons must perfectly isolate the ergols, particularly the hydrogen, from the turbine compartment.
If this function is not ensured, the hydrogen accumulates at the level of the motor or in the interstage space if it is a motor used in one of the upper stages of the launcher, and there is a high risk of explosion when the motor is ignited.
(b) operation:
During the whole operating time of the motor, the sealing means must allow the hydrogen passing through the bearings to be discharged towards the turbine compartment and in addition, with certain lubrication systems, it must fix the hydrogen flow at a predetermined value necessary for the correct operation of the bearings.
From the foregoing, it is clear that the turbine sealing means is particularly critical and its design must therefore allow sure and reliable operation.
The sealing means at present used are of several types:
labyrinths PA1 facial contact seals, PA1 facial retractible seals PA1 floating rings PA1 segmented seals. PA1 non possibility of hydrogen leak to the turbine during the cold period, PA1 reduced consumption of the pressurization gas, PA1 control of the hydrogen flow to the turbine, PA1 increased life span, PA1 reduced size and weight, PA1 greater reliability.
The above mentioned elementary means are used singly or else different combinations of two or more of them are used. Certain assemblies are pressurized, others use hydrodynamic effects.